This invention relates generally to one-way clutches and more particularly to one-way roller clutches that have energizing springs that bias the rollers toward an engaged position where the rollers are wedged between the races so that one race drives the other in one direction.
One-way roller clutches typically have energizing springs, generally accordion shaped, biasing the rollers toward an engaged position wedged between cam surfaces of one race and a cylindrical surface of an associated race. Examples of such one-way roller clutches are shown in U.S. Pat. No. 3,760,914 for a Roller Type Freewheel Clutch granted to Werner W. Gelbrich Sep. 25, 1973; U.S. Pat. No. 3,917,036 for a Molded Cage for an Overrunning roller Clutch granted to Lawrence P. Johnson and Oscar G. Kitchen Nov. 4, 1975 and UK Patent Application GB 2 229 236 of NTN Corporation for a Clutch with Torque Limiter published Sep. 19, 1990.
The purpose of applying a spring force to the rollers is to keep the rollers at an incipient engagement position when the one-way roller clutch is overrunning so that the roller clutch engages immediately upon torque reversal for all operational speeds. However, the above examples and other known one-way roller clutches cannot accomplish this purpose completely because constant rate energizing springs are used. These constant rate energizing springs apply a linearly increasing spring force to the rollers to counteract the centrifugal force of the rollers that increases exponentially with rotational speed. The centrifugal force in fact increases in proportion to the square of the rotational speed. This mismatch produces roller displacements away from the incipient engagement position and lift offs from the raceway surface that increase in proportion to the square of the rotational speed. The response time for clutch engagement upon torque reversal varies and increases in proportion to the roller lift off distance.
The roller displacements and response time can be reduced at higher speeds by increasing the initial bias of the constant rate energizing springs. However, this produces high clutch drag and unnecessary wear at lower operating speeds.